TROOPER
09-29-2008, 03:16 PM
Null Or Straight Cable Determination....
One way you can tell them apart is with a multimeter or continuity tester. With a striaght thru serial cable, pin 2 should lead to pin 2 and pin 3 should lead to pin 3.
A null modem cable pin 2 should lead to pin 3 and pin 3 should lead to pin 2.
If straight thru then all pins should point to the same number on the other end.
and the 2ed way is to test if a cable is a null modem cable is by using window's Hyperterminal utility. Since most computers come with 2 legacy serial ports you can plug both ends of the cable into both serial ports. Than fire up 2 instances of hyperterminal and connect the first instance using com 1 and com 2 for the second instance using the same port settings for both. If the cable is a null modem cable than whatever you type in the one terminal will magically appear in the next terminal.
Your local rat shack or?? has a replacemenrt adapter for under $10.00 , Part # 26-0264 ~ female DB9 to male DB9 ~ pins 5 straight & 2 & 3 crossed ..
Want to know what cable you need to flash that shiny,new receiver ? There are two types of cables used, and both look the same on the outside, but are wired differently internally. They are the straight DB9 RS232 female to female cable, and the Null 9 pin RS232 female to female cable. The straight DB9 cable has all pins connected the same at both ends(pin 1-1, 2-2,3-3,etc.). The Null cable(also known as a Null-Modem) has pins 2 and 3 crossed(pin 2-3, 3-2). You can use a straight DB9 cable to program receivers requiring a Null cable, by purchasing an inexpensive Null adapter to attach to one end of the straight DB9 cable. This allows one cable to be used for any receiver.
*an added note--the gender (male or female) on the connections will not tell you if the cable is NULL or Straight Thru. It can be either gender on each different cable.
One way you can tell them apart is with a multimeter or continuity tester. With a striaght thru serial cable, pin 2 should lead to pin 2 and pin 3 should lead to pin 3.
A null modem cable pin 2 should lead to pin 3 and pin 3 should lead to pin 2.
If straight thru then all pins should point to the same number on the other end.
and the 2ed way is to test if a cable is a null modem cable is by using window's Hyperterminal utility. Since most computers come with 2 legacy serial ports you can plug both ends of the cable into both serial ports. Than fire up 2 instances of hyperterminal and connect the first instance using com 1 and com 2 for the second instance using the same port settings for both. If the cable is a null modem cable than whatever you type in the one terminal will magically appear in the next terminal.
Your local rat shack or?? has a replacemenrt adapter for under $10.00 , Part # 26-0264 ~ female DB9 to male DB9 ~ pins 5 straight & 2 & 3 crossed ..
Want to know what cable you need to flash that shiny,new receiver ? There are two types of cables used, and both look the same on the outside, but are wired differently internally. They are the straight DB9 RS232 female to female cable, and the Null 9 pin RS232 female to female cable. The straight DB9 cable has all pins connected the same at both ends(pin 1-1, 2-2,3-3,etc.). The Null cable(also known as a Null-Modem) has pins 2 and 3 crossed(pin 2-3, 3-2). You can use a straight DB9 cable to program receivers requiring a Null cable, by purchasing an inexpensive Null adapter to attach to one end of the straight DB9 cable. This allows one cable to be used for any receiver.
*an added note--the gender (male or female) on the connections will not tell you if the cable is NULL or Straight Thru. It can be either gender on each different cable.